This invention relates to selenium-base photosensitive materials for electrophotography and more particularly to photosensitive materials comprising selenium or selenium alloys prepared by depositing selenium or selenium alloys or super-finish treated substrates.
Conventionally, the selenium-base photosensitive materials for use in electrophotography are prepared by depositing a thin layer of selenium or selenium-base photoconductive material on a conductive substrate by vacuum evaporation, or the like.
The photoconductive layer of the selenium or selenium alloy photoconductors (hereinafter simply referred to as the "selenium layer") is electrically charged and is then exposed to a light image pattern, thus a latent electrostatic image is formed on the photoconductive layer. During this process, charge carriers move through the selenium layer and the conductive substrate.
Therefore, the characteristics of the photosensitive members are affected greatly, particularly by the condition of the boundary surface between the selenium layer and the substrate.
Aluminum-base materials, stainless steel or the like have been used as the materials of the substrates for use with selenium or selenium-base photoconductors. In particular, aluminum-base substrates are most commonly used since they are inexpensive and easy to handle.
In the case of a mirror-finished substrate, it has a shortcoming of being difficult to handle because a deposoted selenium layer is easily peeled off the substrate by a slight shock or vibrations.
Therefore, various studies have been made to improve the adhesive property between selenium photoconductive layers and substrates. For example, as disclosed in Japanese Published Patent No. 44-32468, there is a method of placing an organic adhesive layer on a substrate as an intermediate layer and then depositing a selenium layer on the intermediate layer by vacuum evaporation.
However, this method involves very difficult technical problems. For instance, in producing such a photoconductive member, it is difficult to form a uniform organic adhesive layer. Moreover, the vacuum degree during vacuum evaporation of selenium is lowered by the emission of gases from the organic adhesive layer due to the heating of the substrate during the vacuum evaporation and also the selenium layer is apt to be contaminated with some impurities from the organic adhesive layer.
When the above mentioned selenium photosensitive materials is used in the conventional electrophotographic processes, such as Carlson process, some traps are apt to be generated, which trap electric carriers in the organic adhesive layer and the selenium layer, inevitably causing the generation of residual potential.
As can be seen from the above example, the attempt of increasing the adhesiveness between the substrate and the selenium layer, by placing such an intermediate layer in between, involves not only the problem of impairing the electrostatic characteristics of the photosensitive materials, but also the difficulty in making a suitable selection of organic materials for use in the intermediate adhesive layer.
Another method of improving the adhesiveness between the substrate and the selenium layer is the making of the surface of substrate uneven or rough so that the adhesion between the selenium layer and the substrate is improved.
As a method belonging to this method, there is a liquid honing process, in which water containing dispersed abrasive particles is injected against the surface of a substrate. Locally, the surface is made rough enough by this method and accordingly the adhesion between the substrate and a selenium layer is appreciably increased. However, a problem with this is that it causes the substrate to have a rather long periodical undulation on the surface. Thus, even if a selenium layer was formed on this substrate, it is not always an uniformly thick, with the result that it has adverse effects on image formation. Moreover, in case the surface of a substrate is made excessively uneven, the electrostatic characteristics of the selenium photosensitive material, such as the surface electric potential (hereinafter referred to as the surface potential) thereof, are impaired.
In this case, the problem is at what surface potential (V) the photosensitive member should be used since in actual copying apparatus, the maximum permissible roughness of the substrate is determined by the surface potential required.
In general, it is said that a photosensitive material with not more than 1250 V of surface potential and with not more than 0.80 of dark decay ratio is not suitable for use.
Furthermore, when the photosensitive material is re-used, the selenium layer has to be peeled off the substrate. In this case, when the substrate is too rough, the peeling off of the selenium layer becomes difficult.
Therefore, the liquid honing method has shortcomings, such as occurrence of a rather long periodical undulation on the surface of a substrate and the difficulty in balancing the increased adhesiveness of the selenium layer with reduction of difficulty in the peeling off of the selenium layer when re-used.